1. Field of the Invention
The field of the invention relates to passive damping devices for reducing vibrations of a building structure responsive to seismic vibrations or the like.
2. Description of the Related Prior Art
The related prior art includes a variety of active seismic response control systems developed for the safety of structures by incorporating earthquake-resisting variable rigidity elements in the column-and-beam frames of structures, such as disclosed in U.S. Pat. Nos. 4,799,339, 4,890,430, 4,922,667, and 4,964,246.
These prior art active seismic response control systems shift the natural frequency of a structure responsive to the detected predominant period of the seismic vibrations so as to render the structure non-resonant. When an earthquake occurs, however, the predominant period is not always easily identifiable, and/or there may be more than one quake to which a response must be made. In active seismic response control systems, various sensors and controlling computers are usually employed. If a dysfunction occurs, failsafe mechanisms are necessary, and such control means can become complicated and costly. Furthermore, the time required to set failsafe control means into operation can cause additional problems.